The invention is particularly concerned with two-cycle internal combustion engines which are commonly provided with transfer passages and porting providing for delivery of fuel from the crankcase into the combustion chamber above the piston. Intake porting is provided in order to introduce fuel into the crankcase space for compression therein upon the downward stroke of the piston and for delivery from the crankcase space through the transfer passage means. Intake valves are commonly provided in the intake passageway or intake tract.
In two-cycle engines of the kind referred to, a crankshaft is provided, being housed in a crankcase below the cylinder, and the crankshaft is connected with the piston working in the cylinder by means of a wrist pin, the axis of which parallels the axis of the crankshaft. This geometry of these parts is well-known; and it is also known that with this geometry, the body of the piston is positioned and supported during its reciprocation in the cylinder by interengagement of surfaces of the piston with the cylinder wall. The principal guiding support for the piston in the cylinder is derived from interengagement of surfaces of the piston body with the cylinder wall in areas concentrated in a plane perpendicular to the axis of the wrist pin; and the wear at the inner surface of the cylinder is correspondingly concentrated in the areas of the cylinder wall concentrated in the plane perpendicular to the wrist pin.
In conventional two-cycle engines, for various reasons, it is very common to employ a fuel intake port in the cylinder wall in the region of the plane perpendicular to the wrist pin, in consequence of which the available surface within the cylinder for supporting and guiding the piston is reduced in proportion to the area of the intake port or ports.
The above interrelationship between the position of the intake port and the plane perpendicular to the wrist pin has been found to be convenient in various types of equipment, such as motorcycles, chain saws and other devices, for a variety of reasons, including the fact that the fuel supply system, including for example, a carburetor, intake passage and valves are also conveniently located in positions generally in the plane perpendicular to the axis of the wrist pin.
In efforts to increase the power of the engine, there has been a tendency to multiply or increase the size of the intake port or ports, and to locate such ports in positions which at least in large part confront the piston through at least a substantial part of the piston stroke; and in consequence, the increase in the intake area tends to reduce the surface area of the cylinder serving to guide or support the piston. One undesirable consequence of this is the increase in wear of the remaining areas of the cylinder wall adjacent to the intake port or ports.
Having the foregoing in mind, the present invention contemplates an arrangement in which at least a part of the intake porting is provided in the cylinder wall in the region of the axial plane of the wrist pin, instead of in a region of the axial plane perpendicular to the wrist pin. By locating intake porting in this manner, relatively large intake ports may be provided without impairing the guiding or supporting function of the surfaces of the cylinder lying in the plane perpendicular to the wrist pin. In the arrangement of the invention, it is further contemplated that for purposes of providing communication between the intake porting and the crankcase, the body of the piston is constructed so that the surfaces thereof are spaced away from the cylinder wall in the regions adjoining the axial plane of the wrist pin. In this way, large intake port area may be provided without appreciably impairing the guiding or support of the piston in the cylinder, with consequent reduction in the wear of the cylinder, even when employing increased intake port area.
It is contemplated according to the invention that this "laterally" positioned intake porting may, if desired, be employed in combination with at least some intake porting lying within the plane perpendicular to the axis of the wrist pin. Moreover, it is further contemplated that the laterally positioned intake porting may be supplied with fuel for admission to the engine through passages extended circumferentially through the cylinder wall toward a position in the region of the plane perpendicular to the axis of the wrist pin, in which position a fuel supply chamber, appropriate valves, carburetor, etc. may conveniently be arranged.
By the intake port system of the present invention, it is possible to still further increase the total intake porting area without seriously affecting the support or guiding of the piston in the cylinder.
The present invention is also concerned with improvements in the interrelationship of the porting and the passage arrangements described above in relation to other porting and passage means, such as the transfer ports and passages commonly employed in two-cycle engines. These improvements may still further enhance the delivery of fuel into the combustion chamber and thereby increase the power of the engine.
The increase in fuel delivery and the consequent improvement in operation of the engine are accomplished according to the present invention by providing a novel interrelationship between the intake porting and passages and the transfer porting and passages, according to which the intake porting and passages not only deliver the fuel to the crankcase space, but also deliver fuel by an injector type of action into the transfer fuel flow during the phase of the cycle of operation in which fuel is being transferred from the crankcase to the combustion chamber.
In the arrangements according to the present invention, reed type intake valves are preferably provided in the intake tract, and injector porting or passages are provided in order to deliver fuel from the intake tract substantially directly into the transfer passage means. According to the invention, this may be accomplished in several ways by providing a region of at least one transfer passage intermediate its ends in communication with the intake passage or tract downstream of the valve means. Indeed, in certain arrangements according to the invention, a region of the intake tract downstream of the valve means and a region of at least one transfer passage intermediate its ends are common to each other.
Several embodiments of engines providing improved operation in various aspects as referred to above are illustrated in the accompanying drawings and described hereinafter.